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 // \$G \$D/\$F.go && \$L \$F.\$A && ./\$A.out // Copyright 2009 The Go Authors. All rights reserved. // Use of this source code is governed by a BSD-style // license that can be found in the LICENSE file. // Generate primes up to 100 using channels, checking the results. // This sieve consists of a linear chain of divisibility filters, // equivalent to trial-dividing each n by all primes p ≤ n. package main // Send the sequence 2, 3, 4, ... to channel 'ch'. func Generate(ch chan<- int) { for i := 2; ; i++ { ch <- i // Send 'i' to channel 'ch'. } } // Copy the values from channel 'in' to channel 'out', // removing those divisible by 'prime'. func Filter(in <-chan int, out chan<- int, prime int) { for i := range in { // Loop over values received from 'in'. if i%prime != 0 { out <- i // Send 'i' to channel 'out'. } } } // The prime sieve: Daisy-chain Filter processes together. func Sieve(primes chan<- int) { ch := make(chan int) // Create a new channel. go Generate(ch) // Start Generate() as a subprocess. for { // Note that ch is different on each iteration. prime := <-ch primes <- prime ch1 := make(chan int) go Filter(ch, ch1, prime) ch = ch1 } } func main() { primes := make(chan int) go Sieve(primes) a := []int{2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97} for i := 0; i < len(a); i++ { if x := <-primes; x != a[i] { println(x, " != ", a[i]) panic("fail") } } }